Nature Geoscience contents: September 2015 Volume 8 Number 9 pp655-733

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TABLE OF CONTENTS September 2015 Volume 8, Issue 9 Editorial Correspondence Feature News and Views Progress Article Review Letters Articles Subscribe   Facebook   RSS   Recommend to library   Twitter   Editorial Top An icy past   p655 doi:10.1038/ngeo2531 During several intervals in Earth's history, ice sheets expanded to cover the globe. These glaciations may be intricately linked to the evolution of life. Correspondence Top Disintegration of Apollo lunar soil   pp657 - 658 B. L. Cooper, K. Thaisen, B. C. Chang, T. S. Lee & D. S. McKay doi:10.1038/ngeo2527 Feature Top Snowball cooling after algal rise   pp659 - 662 Georg Feulner, Christian Hallmann & Hendrik Kienert doi:10.1038/ngeo2523 The Earth underwent two snowball glaciation events between 720 and 635 million years ago. The preceding expansion of eukaryotic algae and a consequent rise in emissions of organic cloud condensation nuclei may have contributed to the dramatic cooling. News and Views Top Geomorphology: Undersea river patterns   pp663 - 664 Jeff Peakall doi:10.1038/ngeo2509 Braided channels are rare on ocean floors, but abundant on land. Experiments and theory suggest that deeper flows and rapid overbank deposition restrict braiding in underwater rivers relative to their terrestrial counterparts. See also: Letter by Foreman et al. Atmospheric chemistry: Ozone pollution from near and far   pp664 - 665 Ruth M. Doherty doi:10.1038/ngeo2497 Tropospheric ozone is generated from precursor pollutants, but can be blown far afield. Satellite observations show rising ozone levels over China — and almost stable levels over western North America despite stricter regulations. See also: Letter by Verstraeten et al. Pluto: Glaciology's new horizon   p666 Tamara Goldin doi:10.1038/ngeo2528 Planetary science: Shepherds of Saturn's ring   pp666 - 667 Aurelién Crida doi:10.1038/ngeo2512 Saturn's F ring is chaperoned on both sides by the tiny moons Prometheus and Pandora. Numerical simulations show that this celestial ballet can result from the collision of two aggregates that evolved out of Saturn's main rings. See also: Letter by Hyodo & Ohtsuki Palaeoclimate: Snowball climate conundrum   pp668 - 669 Philip Allen doi:10.1038/ngeo2504 Evidence for a Neoproterozoic Snowball Earth in the sedimentary record has been controversial. A weathered horizon preserved in sedimentary rocks from Svalbard may provide a rare signature of prolonged global glaciation. See also: Letter by Benn et al. Progress Article Top Robust global ocean cooling trend for the pre-industrial Common Era   pp671 - 677 Helen V. McGregor, Michael N. Evans, Hugues Goosse, Guillaume Leduc, Belen Martrat et al. doi:10.1038/ngeo2510 Sea surface temperatures have varied over the past 2,000 years. A synthesis of surface-temperature reconstructions shows ocean surface cooling from ad 1 to 1800, with much of the trend from 800 to 1800 driven by volcanic eruptions. Review Top Constraints from material properties on the dynamics and evolution of Earth's core   pp678 - 685 Christopher Davies, Monica Pozzo, David Gubbins & Dario Alfé doi:10.1038/ngeo2492 The material properties of the Earth's core have been better constrained by recent technical and computational advances. The properties imply that the core was once hot, but is cooling quickly, and the inner core is young. Letters Top Saturn's F ring and shepherd satellites a natural outcome of satellite system formation   pp686 - 689 Ryuki Hyodo & Keiji Ohtsuki doi:10.1038/ngeo2508 Lying beyond Saturn's main rings, the F ring is shepherded by two small satellites. Simulations suggest that this enigmatic configuration can result from the partial disruption of satellites in collisions at the edge of the main ring system. See also: News and Views by Crida Rapid increases in tropospheric ozone production and export from China   pp690 - 695 Willem W. Verstraeten, Jessica L. Neu, Jason E. Williams, Kevin W. Bowman, John R. Worden et al. doi:10.1038/ngeo2493 Tropospheric levels of ozone and its precursors have risen in Asia since 2000. Satellite observations and chemistry-transport simulations suggest that transport of these pollutants to North America partly offsets benefits from stricter regulation. See also: News and Views by Doherty Sources of and processes controlling CO2 emissions change with the size of streams and rivers   pp696 - 699 E. R. Hotchkiss, R. O. Hall Jr, R. A. Sponseller, D. Butman, J. Klaminder et al. doi:10.1038/ngeo2507 Rivers and streams are key sources of CO2. Estimated emissions and aquatic productivity from across the US show that small streams predominantly emit CO2 produced in soils, but the contribution from aquatic metabolism increases with river size. Braiding of submarine channels controlled by aspect ratio similar to rivers   pp700 - 703 Brady Z. Foreman, Steven Y. J. Lai, Yuhei Komatsu & Chris Paola doi:10.1038/ngeo2505 Braided channels are rare in submarine environments, yet common in fluvial systems. Laboratory experiments suggest that the formation mechanisms are the same, but submarine channels are typically not wide enough to promote braiding. See also: News and Views by Peakall Orbitally forced ice sheet fluctuations during the Marinoan Snowball Earth glaciation   pp704 - 707 Douglas I. Benn, Guillaume Le Hir, Huiming Bao, Yannick Donnadieu, Christophe Dumas et al. doi:10.1038/ngeo2502 The presence of dynamic ice sheets during Snowball Earth glaciations is controversial. Geological evidence and ice sheet modelling suggest that ice sheets may have responded to orbital forcing when pCO2 reached a certain threshold. See also: News and Views by Allen Lower edge of locked Main Himalayan Thrust unzipped by the 2015 Gorkha earthquake   pp708 - 711 Jean-Philippe Avouac, Lingsen Meng, Shengji Wei, Teng Wang & Jean-Paul Ampuero doi:10.1038/ngeo2518 Faults are unlocked by earthquakes. Analysis of seismic data from the 2015 Nepal earthquake shows that only part of the Main Himalayan Thrust fault was unzipped by the quake, leaving much of the fault locked and ready to slip in a future event. Experimental demonstration of a semi-brittle origin for crustal strain transients   pp712 - 715 Jacqueline E. Reber, Luc L. Lavier & Nicholas W. Hayman doi:10.1038/ngeo2496 Plate tectonic motions cause faults to slip during earthquakes and through creep. Laboratory shear experiments on semi-brittle rock-analogue materials suggest that such slip could occur via growth of a series of fractures. Watch an audio-visual summary of the paper here Articles Top Substantial glacier mass loss in the Tien Shan over the past 50 years   pp716 - 722 Daniel Farinotti, Laurent Longuevergne, Geir Moholdt, Doris Duethmann, Thomas Mölg et al. doi:10.1038/ngeo2513 Long-term changes of the mountain glaciers in the Tien Shan, Central Asia, are not well constrained. Remote sensing data and glaciological models reveal a 27% decline of glacier mass from 1961 to 2012, linked to increased summer melting. Millennial changes in North American wildfire and soil activity over the last glacial cycle   pp723 - 727 Hubertus Fischer, Simon Schupbach, Gideon Gfeller, Matthias Bigler, Regine Röthlisberger et al. doi:10.1038/ngeo2495 Ammonium levels in Greenland ice cores track changes in soil emissions and wildfires, primarily in North America. Ice-core ammonium records show abrupt increases in wildfire activity during brief warmings in the last glacial period. A record of spontaneous subduction initiation in the Izu-Bonin-Mariana arc   pp728 - 733 Richard J. Arculus, Osamu Ishizuka, Kara A. Bogus, Michael Gurnis, Rosemary Hickey-Vargas et al. doi:10.1038/ngeo2515 How plate tectonic subduction is initiated is unclear. Analysis of sediments and rock cores taken from the Izu-Bonin-Mariana subduction zone trench suggests subduction started spontaneously in this region around 50 million years ago. 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